Reduction of entrainment in bubble cap towers



June 15, 1954 R. G. DONOVAN 2,681,218

REDUCTION OF ENTRAINMENT IN BUBBLE CAP TOWERS Filed July 22, 1950 QoBer'L Q Donovan. Urn/ember Clb bor rzeg Patented June 15, 1954 REDUCTION OF ENTRAINMENT IN BUBBLE CAP TOWERS Robert G. Donovan, M

etuchen, N. .L, assignor to Standard Oil Development Company, a corporation of Delaware Application July 22, 1950, Serial No. 175,363

1 Claim.

The present invention is concerned with improvements in plate columns for use in fractional distillation and other purposes where intimate contact to obtain equilibrium between vapour and liquid is sought, and in which the liquid descending the column is retained to a certain depth on each plate, and the vapours ascending the column are caused to bubble through these layers of liquids.

In practice the fractionating or other columns generally favored are of the bell type in which a solid horizontal plate is provided with a number of vapour pipes covered by bells. In such bell type of bubbler-plate the duty of a plate of given size is practically limited by the total slot area of the bubblers and the total area of the vapour pipes which can be conveniently arranged on the plate, because the Vapour velocity through the slots and the vapour pipes must not exceed a certain maximum figure, otherwise undue entrainment of the liquid will reduce the efiiciency of the column. This upward entrainment of liquid from tray to tray is caused by the unimpeded upward motion of vapour bubbles or jets and the sudden collapse of these bubbles when they reach the surface of the liquid.

The present invention overcomes these disadvantages of the prior art by providing a column plate having the attributes of economical construction and uniform vapour and liquid distribution and which at the same time reduced bubble size and velocity thereby minimizing entrainment.

In order that the present invention may be more readily understood, reference is hereinafter made to the accompanying drawings, in which Fig. 1 is a horizontal cross-section through a column embodying the present invention, one of the plates being shown in plan; and Fig. 2 is a vertical section taken substantially along line 2-2 of Fig. 1 and is fragmentary in character, showing an intermediate portion of the length of the illustrated column. It will be understood that columns embodying the invention are preferably constructed throughout their lengths in accordance with the principles exemplified by the portions illustrated, and they are, of course, provided with suitable connections for supplying and Withdrawing vapour, and so on, as is usual in such towers.

Referring to the drawings, the column here illustrated has a casing l within which as is customary, are arranged a series of plates 2 carrying a plurality of vapour fiues 3 projecting upwardly therefrom and covered with imperforate caps 4. Each of the plates has cooperating therewith an overflow pipe 5 projecting above the plate and extending downwardly adjacent the next lower plate. In accordance with the invention strips of wire mesh 6, -2 inches thick, are suspended lengthwise and crosswise over the open space between rows of caps 4. The wire mesh is immersed slightly below the normal liquid surface. At each point midway between any four adjacent caps, the wire mesh strips overlap giving double thickness which is particularly desirable since the entraining action is most severe at these points. The wire mesh strips are secured in place by a suitable means such as attachment to the bell caps.

In operation, the vapours evolved at the bottom of column I pass upwardly through each plate and are deflected downwardly by caps 4 through the liquid deposited on the plate and in passing upwardly therethrough are split up into a multiplicity of small streams having a diminished velocity by the apertures of the wire mesh 6. Thus any tendency to entrain liquid by the rising bubbles is greatly reduced and the vapour arising from the surface of the liquid on any given plate contains a minimum of entrained liquid.

The nature and objects of the present invention having been thus described and illustrated, what is claimed as new and useful and is desired to be secured by Letters Patent is:

In an apparatus for countercurrent contacting of vapors and liquids, including a contacting column, a plurality of horizontal plates disposed transversely of the column in vertically spaced relation one to another, a plurality of vapor conduits opening upwardly through each plate and terminating thereabove in vertically spaced relation thereto, said conduits arranged in substantially regular radially spaced relation to each other to form two series of substantially parallel spaced rows, wherein the rows of one series angularly intersect the rows of the other series and wherein each conduit is common to two intersecting rows, a bell cap supported over each conduit, and an overflow conduit opening downwardly through each plate having an inlet end at a level above said vapor conduits, in which column a liquid material is passed vertically downward from plate to plate and horizontally across each plate as a layer of liquid having an upper level substantially equal to that of said overflow conduit inlet end, and in which column vapors are passed upwardly through each plate 3 by way of said vapor conduits to be discharged from below said bell caps supported thereover as a plurality of radial streams within said liquid layer which streams are in substantially opposed relation from one cap to another, and wherein said opposed streams tend to produce areas of turbulence in said liquid layer intermediate said vapor conduits and the bell caps thereover, the improvement which comprises means for suppressing turbulence in the liquid layer on a plate in said series of plates and in the areas intermediate said vapor conduits including two series of wire mesh strips of which the individual strips in one series of strips are disposed longitudinally of the space between adjoining rows in one of said series of vapor conduit rows and the individual strips in the other series of strips are disposed longitudinally of the spaces between adjoining rows of the other series of conduit rows, both series of strips being disposed below the level of the inlet end of the overflow conduit from said plate, and with the strips of one series crossing and overlapping the strips of the other series in an area intermediate any group of three vapor conduits consisting of a first conduit which is common to two intersecting rows, a second conduit in one of said intersecting rows, and a third conduit in the other of said intersecting rows, each of said second and third conduits next adjoining said first conduit in their respective rows, whereby turbulence in the areas intermediate any of said groups of vapor conduits is suppressed by a double thickness of said strips, while turbulence in the areas between any two adjoining conduits in the same row is suppressed by a single thickness of one of said strips.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 888,120 Scherfenberg May 19, 1908 1,560,238 Hoyt et a1 Nov. 3, 1925 1,637,947 Kotzebue Aug. 2, 1927 1,748,411 Cooke Feb. 25, 1930 2,000,444 Hechenbleikner May 7, 1935 2,143,015 Kleinschmidt Jan. 10, 1939 

